1. Field of the Invention
The manufacture of pasta having a smooth surface with minimal amount of solid loss during cooking and with minimal amount of stickiness is accomplished by the use of a low shear extrusion process. Low shear extrusion apparatus to produce a pasta with a smooth surface, minimal amount of solid loss during cooking and minimal amount of stickiness is also provided.
2. Description of the Related Art
Pasta is a nutritional food with a very widespread popularity, independent of economic status or ethnic background. Manufacture of pasta in many different manners by many different entities has made the production of pasta a very crowded art.
One of the methods of manufacturing pasta has been to form an alimentary paste of a flour and water and force such paste through a die which shapes the paste into a desired shape. The pasta obtained from such a process may be further treated, i.e., coated with materials such as an edible oil and/or an edible acid and may, alternatively, be directly cooked or dried. Commercially available dried pasta takes nine to twelve minutes to cook for optimal tenderness. Once cooked, the pasta tends to become sticky and to lose organoleptic properties upon standing for any period of time. Other problems with such commercially available pasta is solid loss during cooking. Extruded products do not necessarily have a smooth surface even though they slide through the die channels (or orifices) during shaping of the alimentary paste because we have found that the paste adheres to the material of which the die is made resulting in shear and surface irregularities in the resulting pasta product.
Current pasta dies available on the market include three components: a die holder made of bronze or bronze aluminum with a predetermined number of holes or passages through which a material is extruded, metallic inserts that will fit inside the holes of the die holder, and metallic rings that will hold the inserts inside the die holes. When placed inside in the holes, the inserts are pushed to the bottom of the die holes and fill approximately one quarter (25%) of the total height of the hole.
A discussion of design and performance of pasta dies was published in Cereal Foods World, pages 807-810, by D. Maldari et al in 1993. Therein, not only bronze alloy, but also stainless steel dies with bronze alloy or TEFLON (trademark of duPont, Wilmington, Del.) inserts were described. It was said that the TEFLON inserts were extensively used for pasta dies.
In the Journal of Food Science, Vol. 47, pages 1055-1058, in an article entitled xe2x80x9cTEFLON and Non-TEFLON Lined Dies: Effect on Spaghetti Qualityxe2x80x9d by B. J. Donnelly, it was said that TEFLON-lined dies was used for three basic reasons, namely, (a) it extends the life-time of the dies by reducing wear on the brass and/or steel; (b) it provides a smoother surface to the pasta; and (c) it improves the general appearance of the dried product.
It was said by Donnelly that there was no published information available detailing the relative quality merits of pasta processed through both die forms. The purpose of the Donnelly paper was to review some research that was done in the laboratory on the effect on spaghetti color and cooking quality of processing durum wheat semolina through TEFLON and non-TEFLON lined dies. In addition, scanning electron microscopy (SEM) of the dry and cooked spaghetti was utilized to determine what gross structural differences were present and if these could contribute to quality differences. However, the Donnelly publication lacks any teaching regarding the TEFLON liner.
The patent literature also contains disclosure of methods for making extruded pasta shapes by feeding a feed stock comprising a glutinous flour and water to an extruder that is equipped with a die plate having a plurality of holes and extruding the alimentary paste through the holes in the extruder die plate by internal pressure; See, U.S. Pat. No. 5,089,284, to Irvin et al. The improvement provided by the invention of Irvin et al comprises heating the extruded die plate to a temperature of at least 130xc2x0 F. (about 54xc2x0 C.) and, preferably, about 160xc2x0 F. (about 71xc2x0 C.). In a preferred embodiment, a coating was provided on a portion of the interior of the holes such that heat transfer from the die to the paste is substantially inhibited until the cross section of the hole reached its smallest value. Thus, in the Irvin die, tapered holes were provided in the die and the first portion of the tapered holes extending from the back of the die toward the orifice was provided with a coating material selected from polyvinylidinefluoride and polytetrafluroethylene (xe2x80x9cTEFLONxe2x80x9d from Dupont, Wilmington, Del.). The innermost face of the die plate is also preferably insulated in order to prevent transfer of heat to the unextruded paste.
The coating on a portion of the orifices served to substantially inhibit heat transfer to the paste being extruded until the small cross section of the hole reaches its smallest value, e.g., by coating all but about the last ten to twenty-five percent of the orifices.
Despite these patents and publications, there remains a need to improve the surface smoothness and organoleptic properties, e.g., mouth-feel, color of pasta products made by an extrusion process.
It is an object of the invention to provide pasta products with improved surface smoothness and organoleptic properties by a low shear extrusion process, wherein an alimentary paste comprising flour and water is fed to a screw extruder, which mixes and conveys the paste and pressurizes the paste so as to force the paste through holes of a die.
It is a further objection of the invention to provide an apparatus comprising a barrel, a rotatable screw within the barrel and a die having a plurality of holes at the end of the barrel wherein the holes of the die are 100% lined with a polytetrafluoroethylene (hereinafter xe2x80x9cPTFExe2x80x9d) material.
It is a further objection of the invention to provide a low shear extrusion process, in which an extrudible mass is sheared by various components of the extrusion apparatus, where such components are completely covered with a low friction materials, such as PTFE, which reduces the shear on the extrudible mass.
It is a still further object of the invention to provide an extrusion apparatus comprising an extruder barrel, a rotatable screw contained within said barrel, a screen and a breaker plate, either or both of which are completely covered with a low friction material such as PTFE and a die having die inserts, which die inserts comprise a low friction material, such as PTFE, preventing any contact of the extrudible mass with the walls of the die and, optionally, comprising covering the back of the die with a coating of low friction material, such as PTFE.
These and other objects of the invention will be apparent from the accompanying drawings and the detailed description of the preferred embodiments.